1. Field of the Invention
The invention relates to a method of utilizing a personal navigation device to perform map matching or dead reckoning, and more particularly, to a method of using known positions of identified road signs to augment GPS coordinate data in order to calculate a more precise location of a personal navigation device.
2. Description of the Prior Art
Global Positioning System (GPS) based personal navigation devices are well known and are widely employed as in-car personal navigation devices. Common functions of a personal navigation device include providing a map database for generating navigation instructions that are then shown on a display of the personal navigation device. These personal navigation devices are often mounted on or in the dashboard of a vehicle using a suction mount or other mounting means.
The term “personal navigation device” refers to a device that enables a user to navigate to a pre-defined destination. The device may have an internal system for receiving location data, such as a GPS receiver, or may merely be connectable to a receiver that can receive location data. The device may compute a route itself, or communicate with a remote server that computes the route and provides navigation information to the device, or a hybrid device in which the device itself and a remote server both play a role in the route computation process. Portable GPS personal navigation devices are not permanently integrated into a vehicle but instead are devices that can readily be mounted in or otherwise used inside a vehicle. Generally (but not necessarily), they are fully self-contained—i.e. include an internal GPS antenna, navigation software and maps and can hence plot and display a route to be taken.
Dead reckoning is the process of estimating one's current position based upon a previously determined position, and advancing that position based upon known speed, elapsed time, and course. With respect to GPS navigation devices, dead reckoning allows continued navigation in the event of a loss of GPS satellite reception, or when navigating in conditions that make GPS-based positioning unreliable. Loss of GPS satellite reception occurs when driving through areas with no clear view of the sky, such as when in tunnels. GPS receivers also produce erroneous position information when navigating through dense “urban canyons” surrounded by tall buildings, such as in large cities.
In addition to situations in which GPS satellite reception is lost, there may also be times in which the GPS coordinate data are not precise enough to be able to specifically pinpoint which road a vehicle containing the personal navigation device is traveling on. For instance, there might be two nearby parallel roads, and the vehicle containing the personal navigation device is traveling on one of the parallel roads. However, to a large margin of error in the received GPS coordinate data, the personal navigation device cannot definitely determine which of the two parallel roads that the vehicle is traveling on.
In order to overcome the lack of reliable GPS coordinate data in the situations explained above, a method of utilizing other resources for performing map matching or dead reckoning is needed.